love the span

include/blt/std/ranges.h

@@ -11,6 +11,7 @@
 #include <blt/std/types.h>
 #include <type_traits>
 #include <iterator>
+#include <memory>
 #include <utility>
 #include <limits>
 
@@ -209,10 +210,65 @@ namespace blt
     template<typename C, typename T>
     itr_offset(C, T) -> itr_offset<typename C::iterator>;
     
-    
     inline constexpr std::size_t dynamic_extent = std::numeric_limits<std::size_t>::max();
     
-    template<typename T, std::size_t extend = dynamic_extent>
+    template<typename T, std::size_t extent = dynamic_extent>
+    class span;
+    
+    // https://codereview.stackexchange.com/questions/217814/c17-span-implementation
+    namespace span_detail
+    {
+        // detect specializations of span
+        template<class T>
+        struct is_span : std::false_type
+        {
+        };
+        
+        template<class T, std::size_t N>
+        struct is_span<span<T, N>> : std::true_type
+        {
+        };
+        
+        template<class T>
+        inline constexpr bool is_span_v = is_span<T>::value;
+        
+        // detect specializations of std::array
+        template<class T>
+        struct is_array : std::false_type
+        {
+        };
+        
+        template<class T, std::size_t N>
+        struct is_array<std::array<T, N>> : std::true_type
+        {
+        };
+        
+        template<class T>
+        inline constexpr bool is_array_v = is_array<T>::value;
+        
+        // detect container
+        template<class C, class = void>
+        struct is_cont : std::false_type
+        {
+        };
+        
+        template<class C>
+        struct is_cont<C,
+                std::void_t<
+                        std::enable_if_t<!is_span_v<C>>,
+                        std::enable_if_t<!is_array_v<C>>,
+                        std::enable_if_t<!std::is_array_v<C>>,
+                        decltype(data(std::declval<C>())),
+                        decltype(size(std::declval<C>()))
+                >> : std::true_type
+        {
+        };
+        
+        template<class C>
+        inline constexpr bool is_cont_v = is_cont<C>::value;
+    }
+    
+    template<typename T, std::size_t extent>
     class span
     {
         public:
@@ -224,11 +280,199 @@ namespace blt
             using const_pointer = const T*;
             using reference = T&;
             using const_reference = const T&;
-        
+            using iterator = T*;
+            using const_iterator = const T*;
+            using reverse_iterator = std::reverse_iterator<iterator>;
+            using const_reverse_iterator = std::reverse_iterator<const_iterator>;
         private:
-        
+            size_type size_;
+            pointer* data_;
         public:
+            constexpr span() noexcept: size_(0), data_(nullptr)
+            {}
+            
+            template<class It, std::enable_if_t<extent != dynamic_extent, bool> = true>
+            constexpr explicit span(It first, size_type count): size_(count), data_(&*first)
+            {}
+            
+            template<class It, std::enable_if_t<extent == dynamic_extent, bool> = true>
+            constexpr span(It first, size_type count): size_(count), data_(&*first)
+            {}
+            
+            template<class It, class End, std::enable_if_t<extent != dynamic_extent, bool> = true>
+            constexpr explicit span(It first, End last): size_(&*last - &*first), data_(&*first)
+            {}
+            
+            template<class It, class End, std::enable_if_t<extent == dynamic_extent, bool> = true>
+            constexpr span(It first, End last): size_(&*last - &*first), data_(&*first)
+            {}
+            
+            template<std::size_t N, std::enable_if_t<(N == dynamic_extent || N == extent) &&
+                                                     (std::is_convertible_v<std::remove_pointer_t<decltype(
+                                                     std::data(std::declval<T(&)[N]>()))>(*)[], T(*)[]>), bool> = true>
+            constexpr span(element_type (& arr)[N]) noexcept: size_{N}, data_{arr}
+            {}
+            
+            template<class U, std::size_t N, std::enable_if_t<(N == dynamic_extent || N == extent) &&
+                                                              (std::is_convertible_v<std::remove_pointer_t<decltype(
+                                                              std::data(std::declval<T(&)[N]>()))>(*)[], T(*)[]>), bool> = true>
+            constexpr span(std::array<U, N>& arr) noexcept: size_(N), data_{arr.data()}
+            {}
+            
+            template<class U, std::size_t N, std::enable_if_t<(N == dynamic_extent || N == extent) &&
+                                                              (std::is_convertible_v<std::remove_pointer_t<decltype(
+                                                              std::data(std::declval<T(&)[N]>()))>(*)[], T(*)[]>), bool> = true>
+            constexpr span(const std::array<U, N>& arr) noexcept: size_(N), data_{arr.data()}
+            {}
+            
+            template<class R, class RCV = std::remove_cv_t<std::remove_reference_t<R>>, std::enable_if_t<
+                    extent != dynamic_extent && span_detail::is_cont_v<RCV> &&
+                    std::is_convertible_v<std::remove_pointer_t<decltype(std::data(std::declval<R>()))>(*)[], T(*)[]>, bool> = true>
+            explicit constexpr span(R&& range): size_(std::size(range)), data_(std::data(range))
+            {}
+            
+            template<class R, class RCV = std::remove_cv_t<std::remove_reference_t<R>>, std::enable_if_t<
+                    extent == dynamic_extent && span_detail::is_cont_v<RCV> &&
+                    std::is_convertible_v<std::remove_pointer_t<decltype(std::data(std::declval<R>()))>(*)[], T(*)[]>, bool> = true>
+            constexpr span(R&& range): size_(std::size(range)), data_(std::data(range))
+            {}
+            
+            template<std::enable_if_t<extent != dynamic_extent && std::is_const_v<element_type>, bool> = true>
+            explicit constexpr span(std::initializer_list<value_type> il) noexcept: size_(il.size()), data_(&il.begin())
+            {}
+            
+            template<std::enable_if_t<extent == dynamic_extent && std::is_const_v<element_type>, bool> = true>
+            explicit span(std::initializer_list<value_type> il) noexcept: size_(il.size()), data_(&il.begin())
+            {}
+            
+            template<class U, std::size_t N, std::enable_if_t<
+                    extent != dynamic_extent && N == dynamic_extent && std::is_convertible_v<U(*)[], T(*)[]>, bool> = true>
+            explicit constexpr span(const span<U, N>& source) noexcept: size_{source.size()}, data_{source.data()}
+            {}
+            
+            template<class U, std::size_t N, std::enable_if_t<
+                    !(extent != dynamic_extent && N == dynamic_extent) && std::is_convertible_v<U(*)[], T(*)[]>, bool> = true>
+            constexpr span(const span<U, N>& source) noexcept: size_{source.size()}, data_{source.data()}
+            {}
+            
+            constexpr span(const span& other) noexcept = default;
+            
+            constexpr iterator begin() const noexcept
+            {
+                return data();
+            }
+            
+            constexpr iterator end() const noexcept
+            {
+                return data() + size();
+            }
+            
+            constexpr const_iterator cbegin() const noexcept
+            {
+                return data();
+            }
+            
+            constexpr const_iterator cend() const noexcept
+            {
+                return data() + size();
+            }
+            
+            constexpr reverse_iterator rbegin() const noexcept
+            {
+                return reverse_iterator{end()};
+            }
+            
+            constexpr reverse_iterator rend() const noexcept
+            {
+                return reverse_iterator{begin()};
+            }
+            
+            constexpr const_reverse_iterator crbegin() const noexcept
+            {
+                return reverse_iterator{cend()};
+            }
+            
+            constexpr const_reverse_iterator crend() const noexcept
+            {
+                return reverse_iterator{cbegin()};
+            }
+            
+            friend constexpr iterator begin(span s) noexcept
+            {
+                return s.begin();
+            }
+            
+            friend constexpr iterator end(span s) noexcept
+            {
+                return s.end();
+            }
+            
+            [[nodiscard]] constexpr size_type size() const noexcept
+            {
+                return size_;
+            }
+            
+            [[nodiscard]] constexpr size_type size_bytes() const noexcept
+            {
+                return size() * sizeof(T);
+            }
+            
+            [[nodiscard]] constexpr bool empty() const noexcept
+            {
+                return size() == 0;
+            }
+            
+            constexpr reference operator[](size_type idx) const
+            {
+                return *(data() + idx);
+            }
+            
+            constexpr reference front() const
+            {
+                return *data();
+            }
+            
+            constexpr reference back() const
+            {
+                return *(data() + (size() - 1));
+            }
+            
+            constexpr pointer data() const noexcept
+            {
+                return data_;
+            }
+            
+            constexpr span<T, dynamic_extent> first(size_type cnt) const
+            {
+                return {data(), cnt};
+            }
+            
+            constexpr span<T, dynamic_extent> last(size_type cnt) const
+            {
+                return {data() + (size() - cnt), cnt};
+            }
+            
+            constexpr span<T, dynamic_extent> subspan(size_type off, size_type cnt = dynamic_extent) const
+            {
+                return {data() + off, cnt == dynamic_extent ? size() - off : cnt};
+            }
+        
     };
+    
+    template<class T, std::size_t N>
+    span(T (&)[N]) -> span<T, N>;
+    
+    template<class T, std::size_t N>
+    span(std::array<T, N>&) -> span<T, N>;
+    
+    template<class T, std::size_t N>
+    span(const std::array<T, N>&) -> span<const T, N>;
+    
+    template<class Cont>
+    span(Cont&) -> span<typename Cont::value_type>;
+    
+    template<class Cont>
+    span(const Cont&) -> span<const typename Cont::value_type>;
 }
 
 #endif //BLT_RANGES_H